CN1839227B - Multi-stage AP mechanical pulping process with refiner flow line treatment - Google Patents

Abstract

This invention combines the steps of adding a chemical substance, such as an alkaline peroxide, to an intermediate pipeline after refining, and the steps of pretreating with the chemical substance, such as an alkaline peroxide, before primary refining, and/or using the chemical substance, such as an alkaline peroxide, in the primary refiner. A preferred embodiment is carried out in a tank, wherein the raw material is refined into pulp in a pressure refiner, and the chemical substance is added after the refinement spray pipe.

Description

Alkaline peroxide mechanical pulping method

technical field

The present invention relates to a process for producing pulp from lignocellulosic matter such as wood chips or the like by means of chemi-mechanical pulping.

Background technique

The use of alkaline peroxide chemicals (APMP) in mechanical pulping systems dates back to 1962. Since then, a number of different process designs have been developed to apply chemicals at the pre-refiner stage, or between stages of refiner refining. In recent years, extensive and systematic studies have been carried out on how different chemical treatments in the mechanical pulping of the refiner affect pulp properties and processes. For hardwoods, alkaline peroxide (AP) pretreatments generally result in better optical properties, better bleaching rates and Higher pulp yield at similar strength. Application of alkaline peroxide prior to refining results in higher specific bulk for a given tensile strength of some hardwood species compared to hydrogen peroxide post-bleaching processes.

Broadly speaking, in the pulping process of alkaline peroxide refiner mechanical pulping, hydrogen peroxide, different types of A hydrogen peroxide stabilizer is applied to the lignocellulosic material. In the early days of this pulping process, two methods were used. One of these is the process of applying alkaline peroxide to the wood chips and completing or nearly completing the bleaching reaction before bleaching; the other is using all alkaline peroxide in the refiner, Alkaline peroxides for pulpers are either not pretreated or pretreated with a stabilizer or other alkali before application.

Typically, the addition of chemicals such as silicates prior to the refiner will lead to a situation where scale is formed on the processing equipment. Scale can also form in the area of the refiner itself due to the formation of silicate deposits, especially when processing softwoods, which can lead to polishing of the disc surface of the refiner.

It has also been proposed to apply chemicals at a point downstream of the refiner. However, these options do not bypass the use of chemical pretreatments or wood chips. In addition, this downstream addition of chemicals is not compatible with the high pressures of refining.

Contents of the invention

In order to achieve a relatively better bleaching efficiency, the present invention introduces the chemicals directly into the lignocellulosic mass immediately after refining, compared to when the chemicals are applied at or upstream of the refiner.

The introduction of chemicals downstream of a refiner, which can be a primary, secondary and/or tertiary refiner, is applied in conjunction with processes using chemicals such as pretreatment of lignocellulosic material with alkaline peroxides prior to refining pulper. Preferably, in order to obtain the advantages of high pressure refining, the refiner is provided with a high pressure vessel.

According to the present invention, the introduction of chemicals downstream of the refiner can optionally be applied together with a process for APMP called P-RC (Post-Treatment Mixer Chemical Treatment), which combines two concepts, one The concept is to pre-treat the lignocellulosic feed with chemicals such as alkaline peroxides before primary refining, and another concept is to apply chemicals such as alkaline peroxides in the primary refiner.

A preferred embodiment of the invention involves the use of more than one-third of the total alkaline peroxide (and/or other known in the art for bleaching) at or near the blow valve in the intermediate line of the post refiner. chemicals or other chemicals for processing lignocellulosic matter into pulp or pulp precursors), and the addition of chemicals to the refiner and chemical impregnation of the sheets upstream of the refiner, resulting in a more energy-efficient process, and the use of There is a better bleaching efficiency before the chemicals are discharged from the refiner.

The main benefit of the present invention compared to conventional technology is that it has a good chemical efficiency by moving more of the chemical reactions downstream, thus performing relatively heavy or more chemical reactions in the post-refiner blowpipe Addition of substances and/or addition of chemical stabilizers.

A further benefit of the present invention is the reduction of the adverse effects of high temperature and/or other conditions during or prior to high pressure primary refining, which are known to affect pulp brightness and formation.

Another benefit of the present invention is that more high-quality steam and/or heat can be obtained compared to other types of P-RC APMP systems, due to being carried out in a high-pressure system, where the primary refiner is fully vented to atmosphere The or import is open to the atmosphere.

Description of drawings

The present invention is better explained and illustrated by the following drawings, in which:

Figure 1 shows the flow chart of the general P-RC APMP process.

Figure 1A shows a flow chart of the steps of feeding lignocellulosic matter to a refiner provided with a vessel at atmospheric pressure, and discharge at atmospheric pressure.

Figure 1B shows a flow chart of the steps of feeding lignocellulosic matter to a refiner provided with a pressure vessel at atmospheric pressure, and discharge at pressure.

Fig. 1C shows a flow chart of conveying the primary pulp generated in the refiner equipped with a container to the high consistency tower through the conveying equipment under normal pressure.

Fig. 1D shows a flow chart of directly conveying primary pulp produced in a refiner equipped with a vessel to a high consistency tower under normal pressure.

Fig. 1E shows a flow chart of conveying the primary pulp produced in the refiner equipped with a pressure vessel to the high consistency tower through the conveying equipment.

Fig. 1F is a flow chart of a related embodiment of the present invention, showing the steps of transporting primary pulp produced in a refiner equipped with a pressure vessel to a high consistency tower.

Fig. 2 is a comparison table of two prior art and P-RC comparison.

Fig. 3 is the relation curve of energy consumption and freeness in two prior art and P-RC.

Fig. 4 is the relation curve of energy consumption and density in two prior art and P-RC.

Figure 5 is a graph of tension progression in both prior art and P-RC.

Figure 6 is a graph of the progression of cracking in two prior art and P-RC.

Figure 7 is a graph of brightness progression in two prior art and P-RC.

Figure 8 is a graph of the light scattering coefficient of two prior art and P-RC pulps as a function of freeness.

Figure 9 is a comparison table of aspen wood chips treated in atmospheric and pressure vessels according to the P-RC.

Figure 10 is a comparison table for the treatment of birch chips in atmospheric and pressure vessels according to the P-RC.

Figure 11 is a flow diagram of an embodiment of the present invention showing the steps of transferring primary pulp produced in a refiner pressure vessel to a diffusion tower followed by chemical addition in an intermediate line with a control valve.

Figure 12 is a flow diagram of an embodiment of the present invention showing the steps of transferring the primary pulp produced in the refiner pressure vessel to the diffusion tower and adding alkaline peroxide in the intermediate line before the inlet of the separator Chemical material.

Figure 13 is a flow diagram of an embodiment of the present invention showing the steps of transferring the primary pulp produced in the refiner pressure vessel to the diffusion tower with the addition of alkaline peroxide chemicals in the intermediate line of the separator .

Figure 14 is a flow diagram of an embodiment of the present invention showing the steps of transferring the primary pulp produced in the refiner pressure vessel to the diffusion tower and adding alkaline peroxide to the intermediate line discharged from the separator. substance.

Figure 15 is a comparison table of blowpipes and refiner perforations for processing birch and maple wood chips with added chemicals in accordance with the present invention.

Figure 16 is a comparison table of spray pipes and refiner holes for processing spruce and red pine wood chips with chemical addition according to the present invention.

Figure 17 is a comparison table of discharge pipes and refiner perforations for processing wood chips with chemical addition at higher pressures in accordance with the present invention.

Fig. 18 is a flow chart of an embodiment of the present invention, showing the steps of transferring the primary pulp produced in the pressure vessel to the tower through the intermediate pipeline.

Detailed ways

Figure 1 presents a simplified flow diagram of the P-RC alkaline peroxide mechanical pulping (APMP) process. The P-RC process generally uses alkaline peroxides in the chip pretreatment/chip impregnation steps/stages 1, 2 while the material is fed to the primary refiner 3.

The pretreatment steps accomplished in stages 1 and 2 in Figure 1 preferably include one or both atmospheric compression equipment, such as screw presses. Flake material is fed through the inlet, passes through at least one compression zone and one expansion zone, and then exits. A chemically active solution (pretreatment solution) is added to the material, usually decompressed at or near discharge, thereby facilitating penetration of the solution into the material.

Refining step 3 may involve a primary refiner of conventional size and shape, and known operating conditions for chemi-mechanical pulping. Depending on factors such as whether and what type of chemicals are added, the size, construction and operation of the refiner can be adjusted so that the chemicals are not overheated or overtime. In one embodiment of the invention, the pressure ranges from about 15 psi to about 45 psi. Any chemicals added to the refiner are called refiner solution.

The steps performed after primary refining can be performed downstream of the refiner with different levels of chemicals, or upstream of other processes. In one embodiment of the invention, the post refining chemistry is modified by an intermediate line solution addition or an addition to the intermediate line solution. The intermediate pipeline is located between the refiner and the diffusion tower. For example, as shown in Figure 11, an alkaline peroxide solution is used to spray the pulp in the middle line of conduit 30 after discharge or exposure from the refiner. The chemicals may be applied at points near the blow pipe 30 or along the blow pipe 30 .

Blowout pipe 30 may run between the vent valve and the separator in the intermediate line. As shown in FIG. 18, chemicals may also be applied in the intermediate line immediately before the vent valve 40, between the separator 42 and the vent valve before the separator 44, and at the separator 46 and/or immediately after the separator 48. apply afterwards. Separators, such as cyclones, may be used to separate steam/heat/liquid or other combinations of substances in the pulp. Before entering the separator, the pulp has a consistency of about 20%-60% and a temperature of about 80°C-150°C.

Injecting chemicals at the location of the intermediate line may be injected through a hole in the intermediate line or a syringe, such as a nozzle, associated with the line. Nozzles can be placed in various ways along or near intermediate lines to facilitate control of chemical additions. For example, control depends on the effect of additives in the bleaching process and/or processing. The chemicals in the pulp flow can thus be modified and maintained by injection sequence, flow rate, composition and/or duration. Other variables such as how deep the syringe is injected into the procedure, the angle of the syringe, the configuration of the syringe opening and other factors of the syringe installation can be modified to achieve the desired result. Chemical incorporation can be varied by changing the location of chemical incorporation by the pressure used in refining. For example, alkaline peroxide can be introduced immediately after the vent valve (less than a few inches to a few feet), especially in low pressure refining at pressures less than 45 psi. Alkaline peroxide can also be introduced immediately after the vent valve before the cyclone (less than a few inches to a few feet), especially in high pressure refining at pressures greater than 45 psi. In other cases, the alkaline peroxide can be introduced between the cyclone and the vent valve, or even within the cyclone.

Refiners can be primary, secondary and/or tertiary and have a pressure vessel or be fully pressurized from preheat to refiner discharge. The pressure in the refiner helps to force the pulp out of the refiner on discharge. The discharge can be varied or controlled eg by a vent valve. The pressure that helps the pulp exit to the intermediate line can allow the pulp to remain in the portion of the intermediate line for a period of seconds to minutes. The pulp has high velocity and violent turbulence when it flows through the intermediate pipeline. These conditions enhance the mixing between the chemicals and the pulp. Strong turbulence at the end of the pulp flow and high temperature gradients also contribute to the transport of chemicals into the individual pulp fibers and into the fiber walls.

In an example, the pulp may be about 100°C or higher and the chemical liquid may be about 40°C or lower. The solution in the intermediate line preferably ranges from about 10°C to 25°C, but can be as high as 80°C. The use of alkaline peroxide in the intermediate line can reduce the exposure time of alkaline peroxide to high temperature, especially when refining is increased temperature and/or pressure. This addition to the pulp by injection at post-refining aids and facilitates the stabilization and enhanced efficacy of hydrogen peroxide. The use of a superatmospheric refiner system in the intermediate line of the present invention also enables better reuse of the steam/heat/liquid in the pulp. This steam can be diverted through steam line 36 . These characteristics also result in a pulp that is highly free and contains low levels of wood chips. It is well known in the art that higher refining pressures produce low levels of wood chips or clean pulp. In some examples, pressure may be included in or in place of cyclone separator 32 . Pressure helps to increase the reuse of steam/heat/liquid in the pulp.

In an embodiment of the invention, an optimal process affecting hydrogen peroxide efficiency and brightness development can be achieved when the primary refining is fully pressurized. It is called P-RC APTMP in a specific structure, which is different from P-RC APMP in which the vessel pressure in the primary refiner is completely atmospheric pressure or the inlet pressure is atmospheric pressure.

FIG. 1A to FIG. 1F show different embodiments of the P-RC process shown in FIG. 1 . For example, Figures 1A, 1B show that after the material has been pretreated in 1 and/or 2, the addition of solution to the lignocellulosic mass can be more pronounced in the transverse conveyor 10, downstream of the screw press and near the refiner 3 , or in the refiner itself, components of the refiner itself such as the parallel transfer lines 12, the inlet holes 14 on the refiner discs and/or the inlet areas of the refiner disc plates 16. Chemical additions as used herein are "substances added to the refiner", around positions 10, 12, 14 and 16. The refiner in the P-RC process can be provided with an atmospheric pressure vessel 3A or a pressurized vessel 3B, but the inlet of the refiner is usually atmospheric pressure. The discharge from the pre-refining pressurized vessel 20a may be by gravity drop. Either way, the refiner discharge is sent directly or indirectly to a high consistency bleach tower 24 as known in the art (but subject to temperature control).

In one embodiment of the invention, the pretreatment solution, the refiner solution (if present) and the intermediate line solution are chemically reacted in the lignocellulosic mass. Depending on the lignocellulosic material and processing equipment, it may be beneficial to modify the material's exposure to chemical agents in order to optimize the process, and/or eliminate or reduce undesired chemical effects and damage. This chemical modification can be accomplished through the sequential addition of chemical additives throughout the process and can be combined with other varying conditions such as temperature, concentration, pressure and duration to further enhance the beneficial effect.

Lignocellulosic matter treated with the P-RC process may be discharged from the primary refiner vessel (atmospheric discharge 20 or pressurized discharge 20a) as primary pulp with measurable freeness, which may be properly referred to as being capable of forming manual pulp. Paper pulp. As shown in Figures 1C and D, the atmospheric discharge from the refiner can be conveyed into the tower 24 by a conveying device 22, such as a screw conveying device, or more directly conveyed 28 by a chute or similar device. In the pressurized vessel, as shown in Figures 1E and F, the refined pulp can usually be vented through a vent valve, directly or indirectly sent to the tower. Optionally, as shown in Figures 1C and E, the pulp bleached in the tower can be further processed eg in a secondary refiner. The high concentration of the diffusion column 24 allows the chemical bleaching reaction to continue from upstream of the column.

In one embodiment of the invention, as shown in Figure 15, the effluent from the vent valve can be passed through a separator and/or pressure indirect transfer channel to a diffusion column.

A large amount of alkaline peroxide in the primary refiner (displacing a large amount of chemical reaction to the chemical treatment stage of the refiner) improves efficiency. This is because variations in chip shape and quality, in addition to differences in the natural nature of the chips and fibers, if not impossible, often make it difficult to obtain a good chemical distribution during the pretreatment/soaking phase of the chips. In these cases, the mixing reaction in the primary refiner helps to improve the chemical distribution and thus the chemical efficiency.

According to an embodiment of the present invention, a pressurized refiner and a higher temperature can be used to refine the pulp by adding chemical substances to the post-refining intermediate pipeline. For example, adding chemicals in the middle of the blowpipe helps provide quicker and more immediate distribution of chemicals, such as hydrogen peroxide, to the color traps for effective bleaching. This efficiency is achieved because the targeted hydrogen peroxide reaction reacts quickly at the beneficial reaction site and does not spread to a more uniform location in the pre-process section. Usually, the inlet temperature between the refiner plates removes the color traps and allows the hemicellulose alkali reaction to proceed very quickly, thereby reducing the pH prematurely. According to another embodiment of the present invention, chemical mixing is carried out in the intermediate pipeline of post-refining, so that the chemical substances are distributed quickly, which is largely sufficient to overcome the temperature rise of the pulp. Such a temperature rise is, for example, about 80°C to 155°C.

In one embodiment of the invention, the pulp may be maintained in an interstage high consistency diffusion tower. The consistency of the pulp in the high consistency diffusion tower is about 20%-40%, preferably about 30%. The temperature of the pulp in the high consistency diffusion tower is about 60°C-95°C. Depending on the chemical reactions required for the chemical treatment, the pulp can remain in the diffusion tower for about 30 minutes to 2 hours. Holding conditions, including but not limited to temperature, pressure, pH, chemical concentration, solids concentration and time, can control and/or bleach the pulp so as to continuously limit the decomposition of the bleaching agent by reactions unrelated to pulp bleaching. Such unrelated reactions can be unproductive, inefficient and/or detrimental to pulp bleaching. For example, depending on the condition and type of lignocellulosic material used in the process, and depending on the type, size and operating conditions of the equipment itself, control of some and/or used conditions may or may not be required. For example, temperature conditions can be altered by the addition of chemicals, pressurized gases, and other heating or cooling methods during the process. The temperature change route can be used during the conveyance of the primary pulp plant 22 by adding water using the mixing screw while the pulp is mixed and conveyed to the tower. If the raw pulp is discharged directly into tower 28, the temperature of the raw pulp can also be adjusted by heating in the tower in a manner known in the art. For example, the pulp can be thermally conditioned by adding liquid or gas, and/or using heat exchangers such as tube, tower, etc. heat exchangers.

The term "control" as used herein should be understood to include both active and passive. Thus, control can be achieved through static hardware configuration or continuous testing of one or more process parameters, and controlling one or more process variables.

The chemical conditions in the inventive process of this invention can be modified by additives to prevent unrelated reactions. For example, such corrections can be carried out in the pretreatment steps 1 and/or 2, as well as in the transverse conveyor 10, the parallel transfer line 12, the inlet holes of the refiner discs 14, the plates on the refiner discs 16, the vent valve 20a , spray pipe 30, separator 32, and/or separator. Examples of stabilizers may be complexation agents. Complexation agents refer to compounds capable of complexing with lignocellulosic matter and metals in the primary pulp to form complex associations known as complexes. These metals include the monovalent metals sodium and potassium, the alkaline earth divalent metals calcium, magnesium and barium, and heavy metals such as iron, copper and manganese. Metal ions retained in the material during processing make oxidative bleaching (such as hydrogen peroxide) less effective, resulting in excessive consumption of chemicals known in the art. To reduce or eliminate the influence of these metal ions in the process, complexes such as diethylenetriaminepentaacetic acid (DTPA), ethylenediaminetetraacetic acid (EDTA) and nitrilotriacetic acid (NTA) can be used. Other known complexing agents in the art can be used alone or in combination according to process conditions. Additionally, silicates and sulfates are known in the art to act as stabilizers, among other functions.

Further embodiments and variants of the present invention can be illustrated by the following examples.

Example

Group A Example

Several different experimental procedures are shown in the following examples. Unless otherwise stated, the materials and conditions for the following examples are as follows: wood; a mix of 50% poplar and 50% basswood for this study. Aspens have rotted centers and are therefore more difficult to bleach than would normally be expected. The wood is sourced from Wisconsin, USA and is debarked, chipped and pre-selected before further processing.

Chemical soaking: wood chips are pretreated with steam for 10 minutes, then soaked in alkaline peroxide chemical liquid, and pressed with Andritz's 560GS single-action disc mill with a compression ratio of 4:1. The chemical liquid was introduced at the release of the pressure and allowed a 30 minute dwell time before refining.

Refining: For all refining, an Andritz 92cm (36″) model 401 twin disc atmospheric refiner was used at a normal speed of 1200rpm. There was a holdover of 15 minutes or more between primary and secondary Time, no solution after primary and before secondary. Refining concentration is 20% in primary and secondary.

Pulp Tests: The pulp tests used were the Society of Pulp, Paper and Industries (Tappi) standards, except freeness, which followed the Canadian Standard Freeness (CSF) test method.

Compare the three processes. In the first process, all alkaline substances (3.3% total alkalinity, (TA) and 2.4% H ₂ O ₂ , and 0.2% DTPA, 0.07% MgSO ₄ and 3% Na ₂ SiO ₃ ) (only one stage of chip soaking was used), followed by refining at atmospheric pressure. Therefore, this "craft" is called "wood chips". The second process uses almost two-thirds of the total hydrogen peroxide chemistry (or _2.4 % TA, 1.6% _H2O2 , 0.08% DTPA, _0.04 % MgSO4 and 2.4% _{Na2SiO 3} ) and used about a third of the chemicals (1.0% TA, 1.0% H ₂ O ₂ , 0.19% DTPA, 0.05% MgSO ₄ and 0.9% Na ₂ SiO ₃ ) in the holes of the primary refiner ; This process is referred to as "wood chip + refiner", representing the present invention. In a third process called "refiner", _the chips are first pressed as in the previous process and then all alkaline peroxide chemicals (4.2% TA, 3.3% _H2O2 , 0.36% DTPA, 0.11% MgSO ₄ and 4.3% Na ₂ SiO ₃ ) were used in the holes of the primary refiner. In all processes, the pulp obtained from primary refining is kept in the drum head for 15 minutes (at a temperature of about 80-90° C.) before the second stage of refining. There is no intermediate wash.

Figure 2 summarizes some process conditions and results for each process. Pulp is obtained by refining in the second stage. In the hydrogen peroxide bleaching stage of mechanical pulping, lower TA/ _H2O2 ratios are generally _preferred at high temperatures to prevent or reduce the possibility of alkaline darkening reactions. For this reason, as shown in Table 1, the lowest TA/ _H2O2 ratio of 1.27 was used for the "refiner" process, the second lowest 1.31 for _the "chip + refiner" process, and the highest 1.37 for the In the "wood chip" process. In the "refiner" process, more TA (4.2%) was used to prevent the pH from dropping too fast or too slow during refining due to the high temperature and heat generated by refining. In Figure 2, reasonable amounts of hydrogen peroxide and pH were maintained in each process.

From a chemical standpoint, the main difference between "chips" and "chips + refiner" is that the latter tends to transfer more of the hydrogen peroxide chemical to the chemical treatment stage of the refiner.

Data collected after secondary refining in the different processes examined are shown in the graphs of Figures 3-8. Figure 3 shows the effect of different chemicals on pulp freeness as a function of the energy consumption rate (SEC), which includes the energy consumed in the chip pretreatment stage. The SEC of "wood chip + process" is slightly smaller than that of "wood chip" process, but the average consumption of SEC of the two processes is about 200kwh/odmt, which is less than that of the refiner bleaching process, although compared with the aforementioned two processes, the latter "refiner Refiner” uses more aggressive chemicals, but has the same residue pH of 8.2 as the “chip + refiner” process. Therefore, the addition of alkaline chemicals in the refiner holes at high temperatures leads to unproductive consumption of more alkali, or to side reactions unrelated to the development of pulp properties.

It should be noted that the SEC of chemi-mechanical pulping of hardwoods in commercial production is generally smaller than that obtained in the laboratory. Therefore, the SEC values in Figure 3 are best used as controls rather than using their absolute values.

Since many pulp properties, especially strength properties, depend on the density of the handsheet, this property was also analyzed by SEC and the results are shown in Fig. 4. In this case, for the more intense refiner chemical treatment P-RC APMP process, the "chip + refiner" process has the best efficiency for the improvement of handsheet density, which is between "chip" and "refiner". The same is true in the "pulp machine" process. These results show that in chemi-mechanical pulping, process energy efficiency depends not only on how much chemicals are used, but also on how they are used.

However, regarding the intrinsic properties of the pulp, there are some differences among the three processes, as shown in Figures 5 and 6, which indicates that the mechanism affecting the fiber strength properties remains the same as long as the chemicals are added before refining.

Regarding the optical properties of pulp, in mechanical pulping, the brightness of pulp is usually related to the beating degree. Figure 7 shows the brightness of different beating degrees in each process. Interestingly, the "chip + refiner" process and the "refiner" process had a similar effect on brightness, even though the former used less bleaching substances, i.e. 2.6% H ₂ O ₂ /3.4% TA vs. 3.3% H ₂ O ₂ /4.2%TA. With all the chemicals added at the soak stage, there are 2 or more points in the "chip" process where the bleaching efficiency is lower than in the "chip + refiner" process. This suggests that bleaching efficiency is sensitive to how chemicals are distributed between chip soaking and refining during the P-RCAPMP process. In this case a comparison of all chemicals added in the chip soaking stage or in the refiner holes was most effective in bleaching and hydrogen peroxide consumption.

Figure 8 shows that there is no difference in light scattering properties among all the processes studied, which indicates that the mechanism of pulp surface formation remains consistent as long as the chemicals are added before refining.

Group B test

The following example shows a different refining configuration in which the pressure test at the inlet of the primary refiner is negligible, the pressure in the vessel (approximately 140KPa). The advantages of this structure are:

1) Better steam treatment when the refiner is discharged, especially a high-capacity refiner (300t/d or higher);

2) It is convenient to transport the primary pulp from the refiner to the middle high consistency (HC) tower;

3) Possibility to use some steam generated in primary refining (separation of steam and pulp fibers by cyclone separator);

4) It is easy to convert the existing TMP system into P-RC APMP process.

These examples show that the same bleaching efficiency is obtained using a primary refiner at a low pressure (140 kPa) vessel and inlet at atmospheric pressure and both vessel and inlet at atmospheric pressure. Before the pulp leaves the vessel and refiner plates, the inlet temperature and the temperature between the primary refiner plates are such that the color traps are removed and the alkaline hydrolysis of the hemicellulose reacts fast enough that the pH is relatively low. Cyclone pulp discharged from the primary refiner was tested in the following examples at a pH range of 9.3-9.7 where hydrogen peroxide tended to be stable even at the high temperatures observed (80-90°C) .

The materials and conditions for the following tests are as follows:

Wood: The wood used in this study was aspen and birch chips purchased from pulp mills in eastern Canada.

Chip Impregnation: A conventional experimental chip impregnation system was used in this study. Of all the P-RC APMPs studied, only DTPA was used in the first stage of chip soaking. The chips are then impregnated with alkaline peroxide (AP) in a second stage. AP treated wood chips are left for 30-45 minutes (without steam) before refining.

Atmospheric refiner system: An Andritz 36″ diameter (92cm) twin-disc 401 system is typically used in the P-RC APMP process under consideration. This system includes an open gauge belt, inclined twin-screw feeder, refiner and open Belt discharge. This system is used for primary and subsequent refining. When used for primary refining, the discharged pulp is collected with a drum, covered with a cover, and placed at a high temperature (usually 80-90°C) a period of time.

Pressurized Refiner System: Andritz single disc 36″ diameter (92cm) pressurized system converted to an atmospheric inlet/pressurized vessel configuration. The original refiner system had the standard features of a conventional TMP system. In order to make the system The inlet is at normal pressure during operation, and a valve is arranged on the top of the vertical steam pipe, and the valve remains open when refining. During the test, the operating speed of the screw plug feeder (PSF) is 50rpm (the normal rotating speed of TMP is 10-20rpm ), so as to ensure that the chemically soaked chips are not compressed. The AP soaked chips are placed in the chip bank, which transports the chips to the blower. Then the chips are blown into the cyclone and discharged to the PSF feed Then the wood chips fall into the vertical steam pipe before entering the refiner. During the refining period, the pressure at the inlet of the primary refiner is controlled to zero, and the pressure in the container is 140KPa. The primary pulp is blown to the cyclone separator , and discharged and collected in drum-shaped drums, and then processed in a similar manner to atmospheric refining.

Pulp test: Brightness test adopts TAPPI standard. Hydrogen peroxide residue was determined by standard iodine titration.

Refining of purchased birch and poplar chips in a primary refiner with a pressurized vessel and atmospheric inlet and in a P-RC APMP was compared. The results showed that the bleaching efficiencies of the two refiners were similar. For some equipment, the use of pressurized vessels can greatly simplify the process, engineering and operation of the P-RC APMP process.

Figure 9 shows the chemical conditions of aspen used in the P-RC APMP, and the brightness obtained in the pressurized and atmospheric vessel primary refiners. Applying similar AP chemistry in both vessels, and similar amounts of total chemical consumption (5.2-5.4% of total alkali, TA, 3.7-3.9% _H2O2 ), atmospheric and _pressurized vessels obtained similar Brightness of 84.2% ISO and 84.7% ISO respectively.

Residue pH (8.8-9.0) in both _vessels was slightly higher than ideal (nearly 7.0-8.5), _H2O2 residue (1.5-2.0% on od pulp) was also higher than normal (0.5-1.0 %), which shows that the pulp properties in both vessels can be further improved if the chemical treatment is optimized.

It should be noted that the bleaching efficiency shown in Table 1 (3.7-3.9% H ₂ O ₂ , consumption of 4% TA, resulting in ISO brightness of 84.2-84.7%) was control or better than that of TMP or CTMP pulp in H ₂ O Bleaching efficiency in ₂ .

Figure 10 shows the results and conditions of P-RC APMP refining for Birch. This particular birch chip is slightly harder to bleach than aspen. Using similar AP chemistry, atmospheric pressure and pressure vessel again _, similar bleaching efficiencies were obtained: 3.1-3.2% TA and 3.4-3.6% _H2O2 , ISO brightness reached 82.4-82.6%. In this _protocol , _the remaining chemicals (0.1-0.2% TA, 0.5-0.6% _H2O2 and pH 8) were within ideal _H2O2 bleaching conditions.

Group C test

This set of experiments shows that, among other factors, when the chemical formulation and distribution are optimized, alkaline peroxide chemicals in the refiner chemical treatment stage can be applied in the intermediate line of a pressurized refiner system to obtain and Imported normal pressure P-RC APMP has similar bleaching efficiency. Due to the short retention time in the intermediate line, the same process can also be used in high pressure refining systems, favoring those operating at 4 bar or higher.

wood

All hardwoods (birch and maple) were processed into chip shapes and blended separately before further processing. All softwoods (spruce, pine and cork mixtures) are processed into round logs, debarked and blended before further processing.

wood chip soaking

Unless otherwise specified, chips were soaked twice in AP chemicals including sodium hydroxide, hydrogen peroxide, DTPA, magnesium sulfate, and sodium silicate in an Andritz 560GS single-action disc refiner system. In some cases, RT-screw presses were used in the first steeping stage (1.4 bar steam treatment for 20 seconds before pressing).

Refining

Andritz 36″ diameter (91cm) single disc 36-1CP refiner system for all pressurized and atmospheric inlet/pressurized vessels, Andritz 36″ diameter (91cm) dual disc 401 system for all atmospheric refining middle. Generally, unless otherwise specified, the 401 refiner is used for all secondary and tertiary refining.

Process Description

The P-RC (pretreatment with refiner chemical treatment with AP chemicals distributed between the chip pretreatment and refiner stages) process was used in all trials performed. For AP chemicals filled in the intermediate line, depending on the specific refining energy used in the refiner, the charge of the chemical and the properties of the raw material, the pulp discharged from the blow pipe is covered in a plastic bag in a round drum Live and keep at 85-95°C.

pulp test

All freeness tests use Canadian Standard Freeness (CSF), and all optical properties tests (brightness Tappi T218 OM-83, light scattering and light absorption coefficient Tappi T425OM-86 (handsheet Tappi 205 OM-88) use the Tappi method.

Figure 15 shows the results of the refiner chemical (RC) treatment stage with AP chemistry applied in the refiner perforations or intermediate lines. Birch and maple were used in this experiment. For each wood species, some chemical pretreatment (pretreatment) is performed on its wood chips. For birch chips, they were treated with 0.3% DTPA in the initial soaking stage, followed by 0.2% MgSO ₄ , 4.4% silicate, 2.8% TA and 2.8% H ₂ O ₂ in the second soaking stage. For maple wood chips, they were treated with 0.5% DTPA in the primary soak stage, followed by 0.1% MgSO ₄ , 2.0% silicate, 1.6% TA, and 2.6% H ₂ O ₂ in the second soak stage. The pretreated wood chips were then treated with a similar amount of AP chemicals in the refiner chemical (RC) treatment stage, but at different sites: one at the refiner eyelets before refining and another immediately after refining intermediate pipeline.

For birch, the two processes (A1 and A2) shared 5.2% _H2O2 and 4.6% total alkalinity ( _TA ), with similar amounts of _H2O2 residue (1.0% _-1.1 %) and final pH (8.9-9.0). The final pH is relatively high, indicating that higher brightness will be obtained if longer retention times are used. Incorporating the AP addition in the refiner eyelets (A1 ) gave similar brightness to the sample compared to adding the AP chemical in the middle line (A2), eg 84.8% versus 84.2% ISO. The slight difference in brightness may be at least partly due to the nuance in their beating, with the former being 285ml in containers and the latter being 315ml. From a chemical point of view, the two processes have similar light absorption coefficients, the former is 0.27m ² /kg, and the latter is 0.25m ² /kg.

For maple, adding the AP chemistry in the middle line (A4) actually gave a higher brightness, ie 81.9% ISO, than applying the AP chemistry in the refiner eyelets (A3), ie 79.2% ISO . The difference in this case is a combination of the former's lower freeness (295 vs. 320 mL) and lower absorption coefficient (0.32 vs. 0.5 ^m2 /kg).

Soft woods, namely spruce and red pine, were also used to examine the effect of different AP chemical applications. Figure 16 summarizes these results and again shows that application of the AP chemistry in the refiner perforations or in the midline gives approximate brightness. For spruce, chips are first soaked with 0.3% DTPA, 0.05% MgSO ₄ , 0.7% silicate, 0.2% TA and 0.5% H ₂ O ₂ , then soaked with 0.1% DTPA, 0.08% MgSO ₄ , 1.8% , 1.4% TA and 1.9% H ₂ O ₂ for a second soak. For red pine, wood chips are first soaked with 0.4% TA, 0.5% H ₂ O ₂ , 0.3% DTPA, 0.04% MgSO ₄ and 0.5% silicate, and then soaked with 0.4% TA, 0.6% H ₂ O ₂ , 0.14% DTPA , 0.05% MgSO ₄ and 0.4% silicate for a second soak. For spruce, for example, as shown in Figure 16, using a similar amount of AP chemistry in the blowpipe process (A6) as process A5 yields similar or slightly higher brightness, i.e. 78.8% ISO vs. 78.2% ISO, where in A5 The latter stage of AP chemistry is used in the refiner eyelets. This slight difference in brightness is again likely the combined effect of their slightly different freeness, ie 47ml vs. 49ml, and the slightly different absorption coefficient of 0.56 vs. ^0.60m2 /kg.

For red pine, the blowpipe process, i.e. A8, has a slightly higher brightness, i.e. 71.8 vs. 71.2% ISO, and a lower light absorption coefficient, i.e. 0.84 vs. 1.01 ^m2 /kg, compared to the refiner perforated process A7 , but has a higher degree of beating, that is, 99 vs. 82mL. For this case, the difference in light absorption coefficient may be caused by the difference in beating degree due to the effect on brightness. The amount of AP chemical treatment was consistent in the two processes.

As shown in Figure 17, a softwood combination of spruce and pine was treated with high pressure during the chemical treatment stage of the refiner. In this case, an RT-screw press was used in the first stage of steeping and an Andritz model 560GS single-action disc mill was used in the second stage. For this chemical treatment, 0.4% TA, 0.6% _H2O2 , 0.18% DTPA, 0.03% _MgSO4 and 0.3% sodium silicate were used for _the first soaking stage; 0.4% TA, 0.7% _H2 O ₂ , 0.15% DTPA, 0.05% MgSO ₄ and 0.4% sodium silicate; in refiner chemical treatment stage with 0.9% TA, 1.5% H ₂ O ₂ , 0.18% DTPA, 0.09% MgSO ₄ and 1.8% silicic acid Sodium, either used in the refiner eyelets of the A9 or in the middle line of the A10. For the processes A9 and A10 used, both had similar chemical charges and formulations, but A9 had a pressure of 2.1 bar in the primary refiner and the other A10 had a pressure of 4.2 bar. The results presented in Figure 17 indicate _that similar bleaching efficiencies and brightness can be achieved in the higher pressure process A10 (with 1.7% TA and 2.8% _H2O2 , and reaching 73.7-73.4% ISO). The samples had similar light absorption coefficients (0.96-1.1 m ² /kg). These results indicate that similar bleaching efficiencies and brightness (in the range of at least 70-75% ISO) can be obtained even at very high pressures (4.2 bar or 60 psi) when the chemistry is optimized. Compared with low pressure, high pressure refining can reuse high quality steam with better efficiency, and for high freeness pulp, there is an opportunity to reduce debris (fiber bundles).

Claims (33)

1. A method of alkaline peroxide mechanical pulping, wherein: the lignocellulosic matter is at least pretreated in a press, and the lignocellulosic matter discharged from the press is soaked with an alkaline peroxide solution when it expands. Refining the pretreated material between two counter-rotating discs in the refiner vessel to form a primary pulp at a temperature of at least 80°C; conveying the primary pulp from the pressure vessel to the intermediate pipeline at a temperature of at least 80°C; adding an alkaline peroxide intermediate line solution to the intermediate line primary pulp when the primary pulp temperature is at least 80°C; mixing the intermediate line solution and the primary pulp to form a reaction mixture in the intermediate line; discharge the reaction mixture at a temperature of at least 80°C into a holding vessel; The reaction mixture was kept in a holding vessel, resulting in a bleached material. 2. The method of alkaline peroxide mechanical pulping according to claim 1, wherein the refiner vessel is under high pressure. 3. The method for alkaline peroxide mechanical pulping according to claim 1, characterized in that the refiner vessel is at normal pressure. 4. The method for alkaline peroxide mechanical pulping according to claim 1, wherein the refiner is a primary refiner. 5. The method for alkaline peroxide mechanical pulping according to claim 1, wherein the refiner is a secondary refiner. 6. The method of alkaline peroxide mechanical pulping according to claim 1, characterized in that the intermediate pipeline is provided with an inlet part, and the alkaline peroxide solution is injected from the inlet part. 7. The method of alkaline peroxide mechanical pulping according to claim 1, characterized in that the intermediate pipeline therein connects the pressure vessel and the pulp retention vessel, and the pulp remains in the retention vessel before further processing. 8. Alkaline peroxide mechanical pulping process according to claim 1, characterized in that the pulp therein is kept for a retention period in an intermediate line before further processing. 9. The method for alkaline peroxide mechanical pulping according to claim 1, characterized in that the material soaked in alkaline peroxide solution after pressing is compressed and expanded again, and is refined in the refiner Re-soak with alkaline peroxide solution before re-soaking. 10. The method for alkaline peroxide mechanical pulping according to any one of claims 1-9, characterized in that alkaline peroxide solution is also injected into the refiner. 11. The method for alkaline peroxide mechanical pulping according to any one of claims 1-9, characterized in that alkaline peroxide is added to the pulp in the intermediate pipeline immediately after the vent valve of the intermediate pipeline solution. 12. The method for alkaline peroxide mechanical pulping according to any one of claims 1-9, wherein said soaking solution contains alkali, peroxide and stabilizer; said intermediate The pipeline solution contains alkali, peroxide and stabilizer; the temperature of the intermediate pipeline solution is less than 80°C. 13. the method for alkaline peroxide mechanical pulping according to claim 1, is characterized in that: conveying the pulp from the vessel to the intermediate pipeline when the pulp temperature is at least 80°C; adding alkaline peroxide to the pulp in the intermediate line when the pulp temperature is at least 80°C; and The intermediate line solution and pulp are mixed to form a reaction mixture in the intermediate line. 14. Process for alkaline peroxide mechanical pulping according to claim 13, characterized in that the reaction mixture having a temperature of at least 80° C. is discharged from the intermediate line into a holding vessel. 15. The method of alkaline peroxide mechanical pulping according to claim 14, characterized in that immediately after the mixing in the intermediate line, the mixture is conveyed to a pulp separator and the separated pulp is then discharged into the in the retention container. 16. The method of alkaline peroxide mechanical pulping according to claim 15, characterized in that the step of adding alkaline peroxide solution to the pulp comprises adding intermediate line solution immediately before the separator. 17. The method for alkaline peroxide mechanical pulping according to claim 1 or 14, characterized in that the temperature range of the pulp transported from the container to the intermediate pipeline is 80°C-155°C, and the concentration is 20-60% . 18. The method of alkaline peroxide mechanical pulping according to claim 17, characterized in that the temperature of the mixture kept in the holding vessel is 60°C-95°C, and the concentration is 20-40%. 19. The method of alkaline peroxide mechanical pulping according to claim 18, characterized in that the reaction mixture is kept in a holding vessel at a temperature of 85°C-95°C, and the concentration is 30%. 20. the method for alkaline peroxide mechanical pulping according to claim 7, is characterized in that: The lignocellulosic substance is wood chips; the refiner is a primary refiner; and Keep the container as a bleaching tower. 21. The method for alkaline peroxide mechanical pulping according to claim 20, characterized in that a separator is provided behind the intermediate pipeline with a vent valve, and alkaline peroxide is added to the primary pulp in the intermediate pipeline The intermediate line solution step involves adding an alkaline peroxide intermediate line solution immediately before the separator. 22. The method for alkaline peroxide mechanical pulping according to claim 20, characterized in that a separator is provided behind the intermediate pipeline with a vent valve, and alkaline peroxide is added to the primary pulp in the intermediate pipeline The intermediate line solution step includes adding an alkaline peroxide intermediate line solution at the separator. 23. The method for alkaline peroxide mechanical pulping according to claim 20, characterized in that a separator is provided behind the intermediate pipeline with a vent valve, and alkaline peroxide is added to the primary pulp in the intermediate pipeline The intermediate line solution step involves adding an alkaline peroxide intermediate line solution after the separator. 24. The method of alkaline peroxide mechanical pulping according to claim 20, wherein the primary pulp bleached in the bleaching tower is further processed into bleached secondary pulp. 25. The method of alkaline peroxide mechanical pulping according to claim 24, characterized in that the bleached secondary pulp is produced by the following steps: Refining primary bleached pulp; discharging secondary pulp from the secondary refiner into an intermediate line provided with at least one solution inlet section; injecting an alkaline peroxide intermediate line solution through at least one solution inlet portion; mixing the intermediate line solution and the secondary pulp in the intermediate line; discharge material from the intermediate line; and The lignocellulose-based material is maintained for a reaction period. 26. The method of alkaline peroxide mechanical pulping according to claim 9, characterized in that the soaking solution contains 0.3% DTPA; the re-soaking solution contains 0.2% MgSO ₄ , 4.4% silicate, 2.8% TA and 2.8% H ₂ O ₂ ; and the intermediate line solution contains 0.16% DTPA, 0.16% MgSO ₄ , 2.3% silicate, contains 0.5% residual 1.8% TA and 2.4% _H2O2 with 1.1% residue _. 27. The method for alkaline peroxide mechanical pulping according to claim 9, characterized in that the soaked solution contains 0.5% DTPA; the re-soaked solution contains 0.2% DTPA, 0.1 % MgSO ₄ , 2.0% silicate, 1.6% TA and 2.6% H ₂ O ₂ ; and the intermediate line solution contains 0.13% DTPA, 0.13% MgSO ₄ , 2.5% silicate , 1.2% TA with 0.1% residue and 2.1% _H2O2 with _2.1 % residue. 28. The method of alkaline peroxide mechanical pulping according to claim 9, characterized in that said soaking solution contains 0.3% DTPA, 0.05% MgSO ₄ , 0.7% silicate, 0.2 % TA and 0.5% H ₂ O ₂ ; the re-soaking solution contained 0.1% DTPA, 0.08% MgSO ₄ , 1.8% silicate, 1.4% TA and 1.9% H ₂ O ₂ and said intermediate line solution containing 0.22% DTPA, 0.11% MgSO ₄ , 1.1% silicate, 0.9% TA with 0.2% residue and 1.2% H ₂ O with 1.7% residue ₂ . 29. The method of alkaline peroxide mechanical pulping according to claim 9, characterized in that said soaking solution contains 0.4% TA, 0.5% H ₂ O ₂ , 0.2% DTPA, 0.04 % MgSO ₄ and 0.5% silicate; the re-soaking solution contains 0.14% DTPA, 0.05% MgSO ₄ , 0.5% silicate, 0.4% TA and 0.6% H ₂ O ₂ and said intermediate line solution containing 0.18% DTPA, 0.06% MgSO ₄ , 1.8% silicate, 1.2% TA with 0.1% residue and 1.8% H ₂ O with 1.1% residue ₂ . 30. The method of alkaline peroxide mechanical pulping according to claim 9, characterized in that said soaking solution contains 0.4% TA, 0.6% H ₂ O ₂ , 0.18% DTPA, 0.03 % MgSO ₄ and 0.3% silicate; the re-soaking solution contains 0.15% DTPA, 0.05% MgSO ₄ , 0.4% silicate, 0.4% TA and 0.7% H ₂ O ₂ and the intermediate line solution containing _1.7 % TA and 2.8% _H2O2 with 1.1% residue. 31. The method of alkaline peroxide mechanical pulping according to claim 2, wherein the pressure in the refiner vessel is kept at least 240KPa. 32. The method of alkaline peroxide mechanical pulping according to claim 31, characterized in that the temperature range of the pulp transported from the container to the intermediate pipeline is 80°C-155°C, and the concentration is 20-60%. 33. The method for alkaline peroxide mechanical pulping according to claim 32, wherein said soaking solution contains alkali, peroxide and stabilizer; said intermediate pipeline solution contains alkali, peroxide substances and stabilizers; the temperature of the intermediate pipeline solution is less than 80°C.

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